The present invention relates to an apparatus for controlling a contact pressure between two rotating members and, more particularly, to an apparatus of each of an inking arrangement and a dampening arrangement of a printing press, which controls a contact pressure between a form roller or a form dampening roller and the surface of a plate mounted on a plate cylinder.
Each of various types of printing presses, e.g., an offset rotary press, has an inking arrangement and a dampening arrangement for supplying an ink and dampening water (to be referred to as water hereinafter), respectively, to the surface of a plate mounted on a plate cylinder. The inking arrangement has an ink fountain roller rotating in an ink fountain containing an ink, and a large number of rollers disposed between the ink fountain roller and the plate cylinder such that their circumferential surfaces contact each other. The ink picked up from the ink fountain upon rotation of the ink fountain roller is uniformly distributed in the respective directions while it is transferred among the rollers, and is supplied to the plate surface on the plate cylinder by the form roller serving as the last one of the rollers.
The dampening arrangement has a water fountain roller rotating in a water fountain containing water, and a plurality of rollers disposed between the water fountain roller and the plate cylinder such that their circumferential surfaces contact each other. Water picked up from the water fountain upon rotation of the water fountain roller is uniformly distributed in the respective directions while it is transferred among the plurality of rollers, and is supplied to the plate surface on the plate cylinder by the form dampening roller serving as the last roller. An image is formed on the plate surface with the ink and water supplied to it, and is transferred on paper directly or through a blanket cylinder, thereby printing the image.
When the contact pressure between the form roller and the plate surface or between the form dampening roller and the plate surface is changed to an inappropriate value as a whole or to cause non-uniformity between the right and left sides of the plate surface, the ink or water attaches to the plate surface excessively, insufficiently, or non-uniformly. Then, a high printing quality cannot be obtained. Therefore, the form roller or the form dampening roller is supported by the free end portions of roller arms, and rotation of the roller arms is adjusted, thereby adjusting the contact pressure.
However, in order to check whether the contact pressure adjustment is appropriately performed or not, conventionally, a piece of paper serving as a gauge is inserted between the form roller or form dampening roller and the plate surface, and the resistance caused when the piece of paper is being pulled out is manually checked. Alternatively, an ink or the like is coated on the form roller, this roller is rotated to transfer the ink or the like on the plate surface, and the width of a thick line transferred on the plate surface is read by a gauge. Thus, the contact pressure cannot be obtained as a quantitative unit of force, and a satisfactory result cannot always be respected.